Image holding member and image forming device

ABSTRACT

The present invention is an image holding member for holding particulate dry process developer by electrical adsorption force, having from the side holding the dry process developer, a dielectric layer, a diffusion reflection layer having reflective fine particles dispersed in a resin and an electroconductive layer. The electrical resistance of the diffusion reflection layer is made smaller than that of the dielectric layer, and/or the ten-point average roughness of the dielectric layer is made 0.1 μm to 5.0 μm. Also, it is an image forming device by use of the above image holding member, having from the side holding the dry process developer, the above image holding member, driving means for the image holding member, recording electrodes arranged in the direction crossing the moving direction of the image holding member and electrically insulated from each other, means for feeding an electroconductive developer between the image holding member and the recording electrodes, and means for applying electrical signals to the recording electrodes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a so called magnestylus system recordingdisplay device which record and display images by attaching a magneticelectroconductive developer onto an image holding member by electricaladsorption force.

2. Related Background Art

In the prior art as the recording display device which enables highlyprecise and large picture face display simply and inexpensively, therehas been proposed the so called magnestylus system (see, for example,Japanese Patent Publication No. 51-46707). Its principle is, as shown inFIG. 5 thereof, to rotate a columnar magnet 2 within a nonmagneticcylinder 3, convey a colored magnetic electroconductive developer 1through its magnetic force on the nonmagnetic cylinder 3 and feed thetoner onto the needle-like recording electrodes 4 arranged densely alongthe axis direction on the nonmagnetic cylinder 3.

And, a voltage is applied according to image information between theelectroconductive layer 7 of an image holding member 5 comprising arecording layer 6 on the surface side and an electroconductive layer 7on the backside nd the recording electrodes 4, to form an image byattaching the magnetic developer 1 onto the image holding member 5 onlyat the portion where voltage is applied.

However, in the case of the prior art as described above, performanceswith respect to high contrast, high life, stability under variousenvironments, high reliability, etc. have been unsatisfactory.

Accordingly, as the method for enhancing the contrast of the imageholding member 5, various methods as shown below have been considered:

(1) a method in which diffusion reflection is effected by making thelight reflecting surface uneven;

(2) a method in which an anodically oxidized film of aluminum is used(see Japanese Patent Publication No. 51-46707);

(3) a method in which a diffusion reflection layer having fine particlesdispersed in a binder resin is laminated on an electroconductive layer7;

(4) a method in which a diffusion reflection layer having fine particlesdispersed in a binder resin and further a dielectric layer are laminatedon an electroconductive layer 7.

However, according to the method of (1), the magnetic electroconductivedeveloper is trapped at the concavities to bring about lowering incontrast.

According to the method of (2), cracks will be generated during anodicoxidatiOn, whereby voltage leak is liable to occur. Also, the surfacebecomes uneven to give rise to similar troubles as in the method of (1).Further, whiteness of the anodically oxidized film is low to make nosufficient contrast. Further, when there is a change in environment,voltage leak will frequently occur, whereby various problems will emergesuch that the density of recording or display is lowered, failing tomake sufficient contrast.

On the other hand, according to the method of (3), although thewhiteness at the initial stage is excellent in contrast, the magneticelectroconductive developer is trapped during repeated uses by the finevoids generated by dispersing fine particles to bring about lowering incontrast.

Also, adsorption and desorption of water are marked at the fine voidportions remaining when the temperature, the humidity, etc. change,whereby electrical resistance will be greatly changed. For this reason,the electrical adsorption force of the developer changes depending onthe environment, whereby there ensues the problem that the change incontrast of image is great. In other works, under highly humidconditions, as the result of adsorption of humidity which progressesremarkably through fine gaps, the electrical resistance is greatlylowered to make the adsorption force of the magnetic electroconductivedeveloper, resulting in lowering of contrast.

According to the method of (4), although whiteness at the initial stageis high and the environmental stability is excellent, whiteness stilltends to be lowered slightly during repeated uses.

SUMMARY OF THE INVENTION

The present invention has been accomplished in order to solve the tasksof the prior art as described above, and its object is to provide arecording display device, in which the so called magnestylus systemwhich records an image on an image holding member by electricaladsorption of a magnetic electroconductive developer, exhibiting highcontrast as well as excellent recording or displaying characteristics.The device further has little environmental dependency and excellentdurability, and an image holding member to be used for such device.

The present invention accomplishing the above object is an image holdingmember for holding particulate dry process developer by electricaladsorption force, having from the side holding the dry processdeveloper, a dielectric layer, a diffusion reflection layer havingreflective fine particles dispersed in a resin and an electroconductivelayer, wherein the electrical resistance of the diffusion reflectionlayer is made smaller than that of the dielectric layer, and/or theten-point average roughness of the dielectric layer is made 0.1 μm to5.0 μm. Also, it is an image forming device by use of the above imageholding member, having from the side holding the dry process developer,the above image holding member, a driving means for the image holdingmember, recording electrodes arranged in the direction crossing themoving direction of the image holding member and electrical insulatedfrom each other, means for feeding an electroconductive developerbetween the image holding member and the recording electrodes, and meansfor applying electrical signals on the recording electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A and FIG. 1 B are schematic sectional views showing the imageholding member of the recording display device according to an exampleof the present invention;

FIG. 2 is a longitudinal sectional view of the pertinent constitution ofthe recording display device in which the image holding device in FIG. 1is used;

FIG. 3 is a longitudinal sectional view showing the whole constitutionof the device in FIG. 2;

FIG. 4 is a whole longitudinal sectional view of the recording displaydevice according to another example of the present invention;

FIG. 5 is a diagram showing the principle of the recording displaydevice of the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, the present invention is described by referring toExamples shown in the drawings.

To illustrate the constitution of the model of the image holding memberin the present invention, it can be as shown in FIG. 1 A and FIG. 1 B.Here, FIG. 1 A shows a structure having a diffusion reflection layer 6alaminated on one surface of an electroconductive support 7 as theelectroconductive layer, while FIG. 1 B shows a structure having adiffusion reflection layer 6a laminated through an electroconductivelayer 7a on one surface of the support 30. And, in either example, onthe reflection layer 6a is laminated a dielectric layer 6b comprisingprimarily a resin.

The surface roughness of the dielectric layer 6b in terms of theten-point average roughness as a measurement distance of 2.5 mm is setat 0.1 μm to 5.0 μm, more desirably 0.1 μm to 3.5 μm. For formation withcontrol of the surface roughness, there may be employed various methodssuch as control of the dispersed state of the reflective fine particlesdispersed in the diffusion reflection layer, addition of coarseparticles, control of flowability during preparation, replica accordingto forms or roughening of the surface layer, etc. As the measuringinstrument, the surface roughness meter manufactured by Taylor Hobson,the universal surface shape measuring instrument "Se-3c" manufactured byKosaka Kenkyusho can be used.

The recording/displaying function by adsorption of magneticelectroconductive developer in the present invention is due to thecharges induced by electrical field into the diffusion reflection layer6a, the dielectric layer 6b, and therefore necessary conditions are thatthe layer between the diffusion reflection layer 6a and the dielectriclayer 6b should have sufficient electrical resistance to not easilybecome under conduction state, or that substantial potential is createdduring charging to function so as to give rise to sufficient contrast.

Accordingly, the state of the image holding member 5 to be functionalmay include some factors depending on the use conditions, but when highcontrast as in the present invention is intended, it is necessary tomaintain 50% or higher of the initial charging voltage at 100 m.sec. ormore after charging, and therefore it is preferable to set theresistivity between the diffusion reflection layer 6a and the dielectriclayer 6b at 10¹² Ω·cm or higher. When higher contrast is, theresistivity between the diffusion reflection layer should be preferably10¹³ Ω·cm or higher. The electrical resistance of the diffusionreflection layer 6a is set at a value smaller than that of thedielectric layer 6b.

In the recording display device of the present invention, its displaycharacteristics are proportional to the charge amount generated in thedielectric layer 6b, and therefore, although slightly related also tothe coloration degree of the magnetic electroconductive developer, as ageneral rule, should desirably satisfy the following relationship inorder to obtain sufficient contrast, when the film thickness between thedielectric layers 6b is made t, the voltage applied when forming displayis made V:

    V>15(V/μm)>t(μm)

Further, for obtaining higher contrast, the relationship may bepreferably:

    V>20(V/μm)>t(μm).

In view of matching with the driving circuit, since a voltage of about100 V or less can be relatively easily outputted, the film thickness ofthe dielectric layer may be practically 7 μm or less, desirably 5 μm orless.

As the resin for forming said dielectric layer 6b, for example, theremay be included thermoplastic resins as represented by polyester,acrylic resin, polyolefin, polyacetal, polyamide, polystyrene, halogencontaining resin, silicone resin, polyether, polycarbonate, vinylacetate resin, fibrin type resin, and copolymers of these, orthermosetting resins as represented by homopolymers or copolymers ofphenol resin, xylene resin, petroleum resin, urea resin, melamine resin,unsaturated polyester, alkyd resin, epoxy resin, silicone resin, furanresin, etc., and these can be also used in a mixture.

Also, into these resins, ion electroconductive substances, ionelectroconductive polymers, electron electroconductive substances,electron electroconductive polymers, etc. can be also added to lowerelectrical resistance.

The diffusion reflection layer 6a comprises reflective fine particlesof, for example, organic resin powder such as styrene resin powder,silicone resin, halogenated olefin resin powder (e.g. polyethylenepowder, polytetrafluoroethylene powder), acrylic resin powder, phenolresin powder, melamine resin powder, etc., or metal oxide such astitanium oxide, magnesium oxide, calcium oxide, barium oxide, zincoxide, tin oxide, antimony oxide, indium oxide, etc., metal sulfate suchas barium sulfate, magnesium sulfate, calcium sulfate, etc., metalcarbonate such as barium carbonate, magnesium carbonate, calciumcarbonate, etc. dispersed in, for example, a single or a mixed resinsuch as a thermoplastic resin as represented by polyester, acrylicresin, polyolefin, polyacetal, polyamide, polystyrene, halogencontaining resin, silicone resin, polyether, polycarbonate, vinylacetate resin, fibrin type resin and copolymers of these, or athermosetting resin as represented by homopolymers or copolymers ofphenol resin, xylene resin, petroleum resin, urea resin, melamine resin,unsaturated, polyester, alkyd resin, epoxy resin, silicone resin, furanresin, etc.

In such recording or displaying method, whiteness has been hithertoinsufficient to give no necessary contrast, but in the presentinvention, since the diffusion reflection layer 6a is constituted of thebinder resin and the reflective fine particles dispersed therein,whiteness of 60% or higher can be obtained to give sufficient contrast.

Also, in the recording display device, since little dependency of thecontrast on the angle vision, namely excellent reflection reflectivityis required, the diffusion reflective light component is required to bemade sufficiently great.

There are several methods for defining the diffusion reflectivity, butin the present invention, for its simplicity and practicability, it isdefined by use of the whiteness based on the following from thereflection density by a Macbeth densitometer or a product of the samefunction.

    ______________________________________                                        Whiteness = [(1.44 - reflection density)/1.44                                             +0.04)] × 100                                               Whiteness 100:                                                                            reflection density ≦ 0.04                                              substantially all members expressed                                           it as pure white in the panel test)                               Whiteness 0:                                                                              reflection density ≧ 1.44                                              (substantially all members                                                    expressed it as black; and also                                               the state where no contrast can                                               be taken at all)                                                  ______________________________________                                    

On the basis of such definition of whiteness, the contrast of recordingor displaying can be defined as the difference between the whiteness asthe image holding member 5 and the whiteness of the recording ordisplaying portion. Therefore, lowering in whiteness of the imageholding member 5 leads necessarily to lowering in contrast to becomeinsufficient as recording or displaying. Also, according to the studies,it has been found that the effect of the present invention will not beimpaired, even if an intermediate layer for enhancing adhesiveness maybe provided in the intermediate between the electroconductive layers 7,7a for prevention of peel-off of the diffusion reflection layer 6a.Also, the electroconductive layers 7, 7a are under electroconductivestate easily with a layer having sufficiently small electricalresistance. In other words, it is a layer which functions so as to giverise to no substantial potential during charging. Accordingly, the stateto be functioned as the electroconductive layer 7, 7a, although theremay be some factors depending on the use conditions, when high contrastis desired as in the present invention, sufficient electroconductionstate may be said to be obtained if decayed after charging to 1/10 ofthe initial charging potential at 100 m.sec. or less, and therefore inthe present Example, resistivity of the electroconductive layers 7, 7ais set at about 10¹² Ω·cm or less.

When more rapid image display is intended, decay after charging to 1/10of the initial charging potential at 1 m.sec. is required, and thereforethe resistivity of electroconductive layers 7, 7a should be desirably10¹⁰ Ω·cm or less.

The material for constituting the electroconductive layers 7, 7a may bea single material or a composite material of an electroconductive metalsuch as aluminum, iron, gold, tin, zinc, etc., an electroconductiveinorganic compound such as carbon, tin oxide, indium oxide, antimonyoxide, etc., or one comprising the above electroconductive substance inthe form of powder in a continuous phase of a polymer, etc.Particularly, for enhancing the contrast as recording or displaying, anelectroconductive layer with little adsorption and excellent in lightreflectivity is desirable.

Next, the magnetic electroconductive developer, which is not a conditionlimiting the present invention, is constituted primarily of a binder,electroconductive powder, magnetic material, and further various dyesand pigments as the colorant, if necessary. As the binder, the binderresin as described above may be used, generally in an amount of 15 to60% by weight.

As the electroconductive powder, fine powder of electroconductivecarbon, various electroconductive metals, fine powder ofelectroconductive oxide such as zinc oxide, tin oxide, indium oxide,antimony oxide, etc. may be used, generally in an amount of 2 to 30% byweight.

As the magnetic material, ferric oxide, etc. may be used in an amount of20 to 80% by weight.

Further, the colorant used if necessary may include dyes or pigments,typically various phthalocyanines, Malachite Green, in an amount of 15to 20% by weight.

By mixing uniformly the various constituent components as describedabove by heating to about 100 ° to 300° C., followed by cooling, andcrushing the mixture into fine powder, and further removing powder withunnecessary particle size by classification, if desired, the objectivemagnetic electroconductive developer can be obtained. This developer hasgenerally an average particle size of about 5 to 20 μm, and one having aresistivity in the range of 10¹³ to 10⁹ Ω·cm at an application voltageof 100 V or lower may be used.

In the following, the present invention is described in more detail byreferring to Examples and Comparative examples. FIG. 2 and FIG. 3 showspecific constitutions of the recording display device.

Numeral 5 is an image holding or bearing member formed as an endlessbelt, which is constituted of the electroconductive support 7 as theelectroconductive layer as described above and the diffusion reflectionlayer 6. The image holding member 5 may be also shaped an a belt whichis not endless. The image holding member 5 is hanged over a pair ofrollers 11, 11' arranged as opposed up and down to each other, supportedflat and movable at the display portion 18 by the back plate 16 and therollers 11, 11', and is moved in the arrowhead direction during imageformation. At the position lowest of the circulating path of the imageholding member 5, namely at the position confronting the roller 11, animage forming means 17 which attaches the magnetic electroconductivedeveloper 1 as the displaying substance onto the image holding member 5according to the display information to form a display image thereon isarranged. The magnetic electroconductive developer 1 is loused in avessel 9.

The information obtained from an original or manuscript reading device15 by the above image forming means 17 is applied through the memorydevice 14 by the recording controlling section 13 as electrical signalsonto the recording electrode 4. Numeral 8 shows transparent plate, 12 acleaning member and 18 a display portion.

As the cleaning member 12, blade cleaning, fur cleaning, suctioncleaning, magnetic brush cleaning, brush cleaning, etc. can be provided.As the cleaning system, the method in which charges induced on the imageholding member surface are electrically removed through the cleaningmember is more effective. For example, the method in which magnets arearranged adjacent to the image holding surface, and theelectroconductive colored magnetic fine powder is interposed to beearthed, or the method by use of an electroconductive brush may beeffectively used.

On the other hand, to introduce general process conditions of therecording display device of the present invention, first, as therotatory magnet 2, one consisting of 6 to 50 poles of 500 to 2000 Gaussis used by rotating at a rotational number of about 300 to 7000 rpm. Asthe nonmagnetic cylinder 3, a nonmagnetic metal such as aluminum,stainless steel, or a molded product of a single substance or acomposite material of plastic or various inorganic oxides is used, andthis may be used either with rotation or under the state not rotated. Asthe recording electrode 4, an application voltage of 10 to 100 V is usedat an electrode width of 0.1 to 1 mm and an electrode distance of 0.1 to1 μm. The moving speed of the image holding member 5 is set at 50 to 700m/sec. and the distance from the electrode 4 at about 50 to 500 μm.

The above image holding member 5 was prepared as follows. First, into 30parts by weight of a polyester resin which is a polycondensate ofterephthalic acid and ethylene glycol, 30 parts by weight of fineparticles of tin oxide with an average particle size of 0.5 μm weremelted and dispersed at 200° C., and the dispersed product was extrudedthrough a T-type die into a film to be heat laminated onto one surfaceof an aluminum foil constituting a 50 μm thick electroconductive layer,to provide a white film with a film thickness of 30μ thereon. Then, bypressurizing by means of a satin-embossed roller controlled to atemperature of 200° C. the roughness of the surface of the white filmwas made 1.5 μm. The diffusion reflection layer was found to have aresistivity of 10⁹ Ω·cm (25° C./50% RH).

Next, a coating material with a viscosity of 10 cps comprising 10 wt. %of a thermosetting phenol resin (number average molecular weight 500)and 90 wt. % of methyl ethyl ketone was coated by a reverse rollercoater under the conditions of a coating speed of 4 m/min. and a gap of10 μm, dried at 140° C. for 5 minutes to provide a dielectric layer witha film thickness of 1 μm on the diffusion reflection layer of theprevious white film, thus providing an image holding member with surfaceroughness of 1.2 μm.

Next, the action of the recording display device of the aboveconstitution is to be described.

The magnetic electroconductive developer used consisted of 30 parts byweight of a bisphenol A type epoxy resin, 10 parts by weight of anelectroconductive carbon and 60 parts by weight of ferric oxide, and hasan average article size of 10 μm and a resistivity of 10⁶ Ω·cm (100 Vapplication).

The rotatory magnet 2 consisted of 16 poles of 900 Gauss, having anouter diameter of 36 φ, and was rotated in the opposite direction to themoving direction of the image holding member 5 at 2200 rpm.

The nonmagnetic cylinder 3 has a thickness of 1 mm, an outer diameter of40, having a polyimide film with a thickness of 200 μm provided with theelectrodes 4 by the etching treatment with an electrode, width of 0.5 mmand an electrode interval of 0.25 mm at the position opposed to theimage holding member 5 adhered onto the outer surface of the nonmagneticcylinder. Application voltage onto the above electrodes 4 is 40 V. Byconveying the image holding member 5 at a speed of 220 mm/sec. undersuch conditions, the display function was examined. The results areshown in Table 1. According to the method as in Example 1, the surfaceroughness of the satin roller was varied variously to prepare rollerswith various surface roughness (0.1 to 5 μm) to provide Examples 2, 3, 4and 5, and further those with surface roughness of 0.05 μm and 5.5 μmare shown as Comparative examples 1 and 2. Also, for clarifying furtherthe effect, one having no dielectric layer provided in Example 1 wasmade Comparative example 3.

                                      TABLE 1                                     __________________________________________________________________________                  Film thickness            Surface roughness**                                 Diffusion                 Diffusion                                           reflection                                                                         Dielectric           reflection                                                                          Dielectric                      Reference No.                                                                         Whiteness                                                                           layer                                                                              layer Environment                                                                           Resistivity***                                                                       layer layer                           __________________________________________________________________________    Example 1                                                                             96    30  μm                                                                             1 μm                                                                          25° C./50% RH                                                                  5 × 10.sup.13 Ωcm                                                        1.5                                                                              μm                                                                            1.2                                                                              μm                        Example 2                                                                             96    30   1     "       5 × 10.sup.13 Ωcm                                                        0.15  0.1                             Example 3                                                                             96    30   1     "       5 × 10.sup.13 Ωcm                                                        0.5   0.4                             Example 4                                                                             96    30   1     "       5 × 10.sup.13 1Ωcm                                                       4     3.5                             Example 5                                                                             96    30   1     "       5 × 10.sup.13 Ωcm                                                        5.5   5                               Comparative                                                                           96    30   1     "       5 × 10.sup.13 Ωcm                                                        0.05  0.05                            Example 1                                                                     Comparative                                                                           96    30   1     "       5 × 10.sup.13 Ωcm                                                        6     5.5                             Example 2                                                                     Comparative                                                                           96    30  none                                                                           "     1 × 10.sup.9 Ωcm                                                          1.5       --                                 Example 3                                                                     __________________________________________________________________________             Initial stage       After successive copying*                                      Nondisplay                                                                              Display       Nondisplay                                                                          Display                                         portion   portion       portion                                                                             portion                           Reference No.                                                                          Contrast                                                                           whiteness whiteness                                                                          Contrast whiteness                                                                           whiteness                         __________________________________________________________________________    Example 1                                                                              96   96        0    93       93    0                                 Example 2                                                                              96   96        0    91       91    0                                 Example 3                                                                              96   96        0    93       93    0                                 Example 4                                                                              96   96        0    93       93    0                                 EXample 5                                                                              96   96        0    91       91    0                                 Comparative                                                                            96   96        0    79       79    0                                 example 1                                                                     Comparative                                                                            96   96        0    69       69    0                                 example 2                                                                     Comparative                                                                            26   96        0     0       50    50                                example 3                                                                     __________________________________________________________________________     *After successive copying; after 10000 repeated display                       **Surface roughness: 10 point average roughness Rz                            ##STR1##                                                                      t: film thickness (diffusion reflection layer thickness) plus (dielectric     layer thickness                                                          

EXAMPLE 6

In this Example, the image holding member 5 was formed by vapordepositing aluminum with a film thickness of 800Å onto the surface of apolyester film with a thickness of 100 μm, coating a coating material toa thickness of 30 μm according to the coating step shown below to form adiffusion reflection layer 6a with a surface roughness of 1.5 μm.Coating of the coating material was performed by dispersing 54 parts byweight of the reducing type electroconductive zinc oxide powder with anaverage particle size of 1.0 μm and 30 parts by weight of athermosetting phenol resin together with 700 parts by weight of methanolfor 10 hours, coating the resulting solution with a dispersed averageparticle size of 1.5 μm by a reverse roll coater, followed by curing at140° C. for 5 minutes. The resistivity of the diffusion reflection layer6a was found to be 1×10⁹ Ω·cm (25° C./ 50% RH).

Next, a coating material with a viscosity of 30 cps comprising 10 wt. %of a soluble vinyl chloride resin (number average molecular weight4×10⁴) and 90 wt. % of methyl ethyl ketone was coated by a reverse rollcoater under the conditions of a coating speed of 4 m/min. and a gap of10 μm, dried at 140° C. for 5 minutes to provide a dielectric layer 6bon the previous diffusion reflection layer 6a of white film, thuspreparing an image holding member 5 with a surface roughness of 1.2 μm.

By controlling the coating conditions for the dielectric layer 6b,Examples 7, 8 with different surface roughness (0.4 μm, 0.1 μm) wereprepared. Together with these Examples and Comparative example 4, thedisplay characteristics of the image holding member 5 are shown in Table2.

                                      TABLE 2                                     __________________________________________________________________________                  Film thickness            Surface roughness**                                 Diffusion                 Diffusion                                           reflection                                                                         Dielectric           reflection                                                                         Dielectric                       Reference No.                                                                         Whiteness                                                                           layer                                                                              layer Environment                                                                           Resistivity***                                                                       layer                                                                              layer                            __________________________________________________________________________    Example 6                                                                             94    30 μm                                                                           1 μm                                                                             25° C./50% RH                                                                  1 × 10.sup.13 Ωcm                                                        1.5 μm                                                                          1.2 μm                                94    "    "     15° C./10% RH                                                                  1 × 10.sup.14 Ωcm                                                        "    "                                        94    "    "     35° C./85% RH                                                                  1 × 10.sup.12 Ωcm                                                        "    "                                Example 7                                                                             94    30 μm                                                                           2 μm       1 × 10.sup.13 Ωcm                                                        1.5 μm                                                                          0.4 μm                        Example 8                                                                             94    30 μm                                                                           3 μm       1 × 10.sup.13 Ωcm                                                        1.5 μm                                                                          0.1 μm                        Comparative                                                                           94     4 μm                                                                           4 μm       1 × 10.sup.13 Ωcm                                                        1.5 μm                                                                          0.05 μm                       Example 4                                                                     __________________________________________________________________________             Initial stage      After successive copying*                                       Nondisplay                                                                             Display      Nondisplay                                                                          Display                                           portion  portion      portion                                                                             portion                             Reference No.                                                                          Contrast                                                                           whiteness                                                                              whiteness                                                                          Contrast                                                                              whiteness                                                                           whiteness                           __________________________________________________________________________    Example 6                                                                              94   94       0    91      91    0                                            94   94       0    91      91    0                                            94   94       0    91      91    0                                   Example 7                                                                              94   94       0    91      91    0                                   Example 8                                                                              94   94       0    89      89    0                                   Comparative                                                                            94   94       0    77      77    0                                   example 4                                                                     __________________________________________________________________________     *After successive copying; after 10000 repeated display                       **Surface roughness: 10 point average roughness Rz                            ##STR2##                                                                      -                                                                             t: film thickness (diffusion layer thickness) plus (dielectric layer          thickness                                                                

Also, in Example 6, by changing the composition ratio of the reducingtype electroconductive zinc oxide used for the diffusion reflectionlayer 6a as shown in Table 3, Examples 9-11 and Comparative examples 5,6 with different resistivities of diffusion reflection layers wereprepared, and their display characteristics are shown in Table 4.

                                      TABLE 3                                     __________________________________________________________________________                                Diffusion                                                 Reducing type       reflection                                                electroconductive                                                                       Thermosetting                                                                           layer inherent                                            zinc oxide powder                                                                       phenol resin                                                                            electric resistance                               __________________________________________________________________________    Example 9                                                                             120 parts by weight                                                                     30 parts by weight                                                                      1 × 10.sup.7 Ω · cm          Example 10                                                                            90 parts by weight                                                                      "         1 × 10.sup.8 Ω · cm          Example 11                                                                            30 parts by weight                                                                      "         1 × 10.sup.12 Ω · cm         Comparative                                                                           15 parts by weight                                                                      "         1 × 10.sup.13 Ω · cm         example 5                                                                     Comparative                                                                           10 parts by weight                                                                      "         1 × 10.sup.14 Ω · cm         example 6                                                                     __________________________________________________________________________

                                      TABLE 4                                     __________________________________________________________________________                  Film thickness             Surface roughness**                                Diffusion                  Diffusion                                          reflection                                                                          Dielectric           reflection                                                                          Dielectric                     Reference No.                                                                         Whiteness                                                                           layer layer Environment                                                                           Resistivity***                                                                       layer layer                          __________________________________________________________________________    Example 9                                                                             94       30 μm                                                                            1 μm                                                                          25° C./50% RH                                                                  1 × 10.sup.13 Ωcm                                                           1.5 μm                                                                           1.2 μm                   Example 10                                                                            94    30    1     "       1 × 10.sup.13 Ωcm                                                        1.5   1.2                            Example 11                                                                            94    30    1     "       1 × 10.sup.13 Ωcm                                                        1.5   1.2                            Comparative                                                                           94    30    1     "       2 × 10.sup.13 Ωcm                                                        1.5   1.2                            Example 5                                                                     Comparative                                                                           94    30    1     "       2 × 10.sup.13 Ωcm                                                        1.5   1.2                            Example 6                                                                     __________________________________________________________________________             Initial stage       After successive copying*                                      Nondisplay                                                                              Display       Nondisplay                                                                          Display                                         portion   portion       portion                                                                             portion                           Reference No.                                                                          Contrast                                                                           whiteness whiteness                                                                          Contrast whiteness                                                                           whitenessptz,1/54                 Example 9                                                                              94   94         0   91       91     0                                Example 10                                                                             94   94         0   91       91     0                                Example 11                                                                             94   94        10   81       91    10                                Comparative                                                                            94   94        40   51       91    40                                example 5                                                                     Comparative                                                                            94   94        60   31       91    60                                example 6                                                                     __________________________________________________________________________     *After successive copying; after 10000 repeated display                       **Surface roughness: 10 point average roughness Rz                            ##STR3##                                                                      -                                                                             t: film thickness (diffusion reflection layer thickness) plus (dielectric     layer thickness                                                          

EXAMPLE 12

In this Example, the image holding member 5 was formed by vapordepositing aluminum with a film thickness of 800Å onto the surface of apolyester film with a thickness of 100 μm, coating a coating material toa thickness of 30 μm according to the coating step shown below to form adiffusion reflection layer 6a with a surface roughness of 1.5 μm. Thatis, coating of the coating material was performed by dispersing 54 partsby weight of antimony oxide powder with an average particle size of 1.0μm and 30 parts by weight of a thermosetting phenol resin together with700 parts by weight of methanol for 10 hours, coating the resultingsolution with a dispersed average particle size of 1.5 μm by a reverseroll coater, followed by curing at 140° C. for 5 minutes. Theresistivity of the diffusion reflection layer was found to be 1×10⁸ •·cm(25° C./50% RH).

Next, a coating material with a viscosity of 30 cps comprising 10 wt. %of a soluble acrylic resin (number average molecular weight 4×10⁴) and90 wt. % of methyl ethyl ketone was coated by a reverse roll coaterunder the conditions of a coating speed of 4 m/min. and a gap of 10 μm,dried at 140° C. for 5 minutes to provide a dielectric layer with a filmthickness of 1 μm on the previous diffusion reflection layer of whitefilm, thus preparing an image holding member with a surface roughness of1.2 μm. One using a soluble type vinyl alcohol resin as the resin forthe dielectric layer 6b was made Example 12, while those using solublevinyl pyridine resin, soluble polyacrylic quaternary amine resin weremade Comparative examples 7 and 8, of which characteristics as therespective image holding members when formed into image holding membersby coating similarly as in Example 12 are shown in Table 5.

                                      TABLE 5                                     __________________________________________________________________________                  Film thickness      Surface roughness**                                       Diffusion                  Diffusion                                          reflection                                                                          Dielectric           reflection                                                                          Dielectric                     Reference No.                                                                         Whiteness                                                                           layer layer Environment                                                                           Resistivity***                                                                       layer layer                          __________________________________________________________________________    Example 12                                                                            93       30 μm                                                                            1 μm                                                                          25° C./50% RH                                                                  1 × 10.sup.14 Ωcm                                                           1.5 μm                                                                           1.2 μm                   Example 13                                                                            93    30    1     "       1 × 10.sup.12 Ωcm                                                        1.5   1.2                            Comparative                                                                           93    30    1     "       5 × 10.sup.10 Ωcm                                                        1.5   1.2                            Example 7                                                                     Comparative                                                                           93    30    1     "       5 × 10.sup.8 Ωcm                                                         1.5   1.2                                     Initial stage       After successive copying*                                      Nondisplay                                                                              Display       Nondisplay                                                                          Display                                         portion   portion       portion                                                                             portion                           Reference No.                                                                          Contrast                                                                           whiteness whiteness                                                                          Contrast whiteness                                                                           whioteness                        __________________________________________________________________________    Example 12                                                                             93   93         0   90       90     0                                Example 13                                                                             88   93         5   85       90     5                                Comparative                                                                            58   93        35   55       90    35                                Example 7                                                                     Comparative                                                                            23   93        70   20       90    70                                Example 8                                                                     __________________________________________________________________________     *After successive copying; after 10000 repeated display                       **Surface roughness: 10 point average roughnes Rz                             ##STR4##                                                                      -                                                                             t: thickness (diffusion reflection layer thickness) plus (dielectric laye     thickness                                                                

As is apparent from the above Examples, according to the presentExamples, excellent contrast, recording or display characteristics,repetition characteristics and environmental stability can be obtained.

The present invention is not limited to the above Examples, but can bepracticed with various modifications within the spirit of the invention.For example, as an example, by equipping the recording device shown inFIG. 3 with the writing display function, the reading function and theprinting function, a recording display device shown in FIG. 4 can beprepared.

The image information to be displayed is inputted from the manuscriptreading device 15, and through the symbolized composite circuit 28 andthe memorizing device 14, or directly from the symbolized compositecircuit 28, applied by the recording control section 13 as electricalsignals on the recording electrode 4.

Also, on the outer peripheral side of the above image holding member 1,is arranged a writing medium 20 which is formed in the shape of anendless belt, transparent and writable as well as erasable with a feltpen, etc., and the writing medium 20 is hanged circulatably over therollers 19, 19' and 19", and supported in flat shape by the rollers 19,19' at the display portion. Also, in the vicinity of the roller 11 areprovided cleaning members 12, 12' for removing the magneticelectroconductive developer attached on the image on the image holdingmember 5 and the back surface of the writing medium 20.

The cleaning members 12, 12' remove the magnetic electroconductivedeveloper by rotating in the shape of a brush the magnet brush of thetoner formed by magnetic attracting force on the outer periphery of thecylindrical members. At the lower side of the roller 19' is arranged anerasing member 21 for erasing the image written on the writing medium20.

Further, on the backside of the image holding member 5 is arranged areading means 22 for reading images on the image holding member and thewriting medium 20. More specifically, at the reading position which isthe nearest position between the image holding member 5 and the writingmedium 20 are arranged a lamp 24 equipped with a reflection hood 23 forirradiating the images on both members 5, 20, and a mirror 27 forpermitting the reflected light images from the both members 5, 20 toenter photoelectric converting element 26 through the lens 25.

The images on the above image holding member 5 and the writing medium 20are read by the photoelectric converting element 26 and recorded throughthe symbolized composite circuit 28, directly or through the memorizingdevice 14 on the printer 29.

According to the Examples as described above, the diffusion reflectionlayer having reflective fine particles dispersed in a resin can removeinner cracks, etc., and therefore can effect alleviation of trapping ofthe magnetic electroconductive developer by the uneven surface, wherebyleak of voltage can be prevented.

Also, since reflective fine particles are dispersed in a resin,whiteness is improved due to the synergetic effect with the interfacereflection from the refractive index difference at such interface toimprove contrast. Further, by providing a dielectric layer on thediffusion reflection layer, fine unevenness due to reflective fineparticles remaining on the diffusion reflection layer surface as well asfine voids internally formed can be removed.

As a consequence, penetration of the magnetic electroconductivedeveloper into fine voids during repeated uses, and lowering in contrastduring repeated uses by securing of fine unevenness on the surface, andfurther lowering in electrical resistance due to adsorption of waterthrough fine voids at high humidity can be avoided, whereby contrastlowering at high humidity can be markedly prevented.

Also, when the dielectric layer of the image holding member directlycontacts the magnetic electroconductive developer, charges are injectedfrom the magnetic electroconductive developer during voltage applicationto result in generation of charges in the dielectric layer. If at thistime the electrical resistance of the diffusion reflection layerconstituting the image holding member is greater than that of thedielectric layer, charge decay at the diffusion reflection layer becomesslower than that in the dielectric layer, whereby the charges injectedinto the dielectric layer will reside at the interface with thediffusion reflection layer to give extremely poor efficiency ofdeelectrification and a potential remaining internally, which may causeghost or contrast lowering during repetition.

In the present invention, since the electrical resistance of thediffusion resistance layer is smaller than that of the dielectric layer,the charges in the diffusion reflectiOn layer will be quickly decayed.As the result, it becomes possible to discharge quickly the chargesremaining internally of the dielectric layer through the diffusionreflection layer to the substrate side, which is very advantageous indecay of residual charges and effective for removing ghost, preventingcontrast lowering during repetition.

Also, if the surface roughness of the dielectric layer is 0.1 μm orless, the surface becomes too smooth, and the dielectric layer directlycontacts the magnetic electroconductive developer and charges areinjected from the magnetic electroconductive developer, with the resultthat the electrical field is liable to remain internally of thedielectric layer, thereby causing readily ghost or contrast lowering tooccur. On the other hand, if the surface roughness of the dielectriclayer is 5 μm or more, the magnetic electroconductive developer istrapped by the unevenness of the surface to be secured on the surface,thus bringing about lowering in contrast.

Accordingly, in the present invention, by setting the surface roughnessin the range of 0.1 to 5 μm, highly insulating void is formed betweenthe dielectric layer and the magnetic electroconductive developer toinhibit charge injection into the dielectric layer, and also thedeveloper will not be trapped by the fine unevenness on the surface.

Table 6 shows Examples 14, 15, 16, 17 and 18 with different surfaceroughnesses (0.1 to 5 μm) prepared by varying the surface roughness ofthe satin-embossed roller according to the same method as in Example 1,and further Comparative examples 9 and 10 with surface roughnesses of0.05 μm and 5.5 μm. Also, for making the effect clearer, one having nodielectric layer provided in Example 14 was made Comparative example 11.

Table 7 shows additionally Examples 19, 20, 21 and Comparative example12 prepared according to the same method as in Example 1 except forslight change conditions, namely with changes in film thickness of thediffusion reflection layer. Also, for making the effect clearer, onehaving no dielectric layer provided in Example 19 was made Comparativeexample 13.

                                      TABLE 6                                     __________________________________________________________________________                Film thickness            Surface roughness**                                 Diffusion                 Diffusion                                       White-                                                                            reflection                                                                         Dielectric           reflection                                                                         Dielectric                         Reference No.                                                                         ness                                                                              layer                                                                              layer Environment                                                                           Resistivity***                                                                       layer                                                                              layer                              __________________________________________________________________________    Example 14                                                                            87  6 μm                                                                            1 μm                                                                             25° C./50% RH                                                                  5 × 10.sup.13 Ωcm                                                        1.5 μm                                                                          1.2 μm                          Example 15                                                                            87  6 μm                                                                            1 μm                                                                             "       5 × 10.sup.13                                                                  0.15 0.1                                Example 16                                                                            87  6 μm                                                                            1 μm                                                                             "       5 × 10.sup.13                                                                  0.5  0.4                                Example 17                                                                            87  6 μm                                                                            1 μm                                                                             "       5 × 10.sup.13                                                                  4    3.5                                Example 18                                                                            87  6 μm                                                                            1 μm                                                                             "       5 × 10.sup.13                                                                  5.5  5                                  Comparative                                                                           87  6 μm                                                                            1 μm                                                                             "       5 × 10.sup.13                                                                  0.05 0.05                               Example 9                                                                     Comparative                                                                           87  6 μm                                                                            1 μm                                                                             "       5 × 10.sup.13                                                                  6    5.5                                Example 10                                                                    Comparative                                                                           87  6 μm                                                                            none  "       5 × 10.sup.13                                                                  1.5  --                                 Example 11                                                                    __________________________________________________________________________             Initial stage       After successive copying*                                       Nondisplay                                                                            Display     Nondisplay                                                                            Display                                           portion portion     portion portion                            Reference No.                                                                          Contrast                                                                            whiteness                                                                             whiteness                                                                           Contrast                                                                            whiteness                                                                             whiteness                          __________________________________________________________________________    Example 14                                                                             87    87      0     84    84      0                                  Example 15                                                                             87    87      0     82    82      0                                  Example 16                                                                             87    87      0     84    84      0                                  Example 17                                                                             87    87      0     84    84      0                                  Example 18                                                                             87    87      0     82    82      0                                  Comparative                                                                            87    87      0     70    70      0                                  example 9                                                                     Comparative                                                                            87    87      0     60    60      0                                  example 10                                                                    Comparative                                                                            87    87      0     30    30      0                                  example 11                                                                    __________________________________________________________________________     *After successive copying; after 10000 repeated display                       **Surface roughness: 10 point average roughness Rz                            ***Resistivity                                                                ##STR5##                                                                      S: measured area,                                                             t: film thickness (diffusion reflection layer thickness) plus (dielectric     layer thickness)                                                         

                                      TABLE 7                                     __________________________________________________________________________                 Film thickness                                                                Diffusion                                                                White-                                                                             reflection                                                                         Dielectric                                                  Reference No.                                                                         ness layer                                                                              layer Environment                                                                            Resistivity***                               __________________________________________________________________________    Example 19                                                                            86   10                                                                              μm                                                                            1  μm                                                                            25° C./50% RH                                                                   1 × 10.sup.13 Ωcm                                        15° C./10% RH                                                                   1 × 10.sup.14                                                  35° C./85% RH                                                                   1 × 10.sup.12                          Example 20                                                                            92   20   1     25° C./50% RH                                                                   1 × 10.sup.13                          Example 21                                                                            96   30   1     25° C./50% RH                                                                   1 × 10.sup.13                          Comparative                                                                           65   2    1     25° C./50% RH                                                                   1 × 10.sup.13                          Example 12                                                                    Comparative                                                                           65   2          25° C./50% RH                                                                   1 × 10.sup.9                           Example 13              15° C./10% RH                                                                   1 × 10.sup.10                                                  35° C./85% RH                                                                   1 × 10.sup.8                           __________________________________________________________________________            Initial stage   After successive copying*                                          Nondisplay                                                                          Display   Nondisplay                                                                          Display                                                 portion                                                                             portion   portion                                                                             portion                                    Reference No.                                                                         Contrast                                                                           whiteness                                                                           whiteness                                                                          Contrast                                                                           whiteness                                                                           whiteness                                  __________________________________________________________________________    Example 19                                                                            86   86    0    81   81    0                                                  86   86    0    81   81    0                                                  86   86    0    81   81    0                                          Example 20                                                                            92   92    0    87   87    0                                          Example 21                                                                            96   96    0    91   91    0                                          Comparative                                                                           65   65    0    60   60    0                                          Example 12                                                                    Comparative                                                                            5   65    60    0   35    35                                         Example 13                                                                             5   65    60    0   35    35                                                  5   65    60    0   35    35                                         __________________________________________________________________________     *After succesive copying; after 10000 repeated display                        ***Resistivity                                                                ##STR6##                                                                      S: measured area,                                                             t: film thickness (diffusion reflection layer thickness) plus (dielectric     layer thickness)                                                         

EXAMPLE 22

In this Example, the image holding member 5 was formed by vapordepositing aluminum with a film thickness of 800Å onto the surface of apolyester film with a thickness of 100 μm, applying a coating materialto a thickness of 30 μm according to the coating step shown below toform a coating as the diffusion reflection layer with a surfaceroughness of 1.5 μm. More specifically, coating of the coating materialwas performed by dispersing 54 parts by weight of barium sulfate powderwith an average particle size of 1.0 μm and 30 parts by weight of athermosetting phenol resin together with 810 parts by weight of methanolin a ball mill for 10 hours, coating the resulting dispersion with anaverage dispersed particle size of 1.5 μm by a reverse roll coater,followed by heating at 140° C. for 5 minutes.

Next, a coating material with a viscosity of 30 cps comprising 10 wt. %of a soluble acrylic resin (number average mOlecular weight 4×10⁴) and90 wt. % of methyl ethyl ketone was coated by a reverse roll coaterunder the conditions of a coating speed of 4 m/min. and a gap of 10 μmand dried at 140° C. for 5 minutes to provide a dielectric layer with afilm thickness of 1 μm on the previous white film of the diffusionreflection layer, thus preparing an image holding member 5 having asurface roughness of 1.2 μm.

Table 8 shows the recording and displaying characteristics of the imageholding member 5 in Examples and Comparative examples with differentsurface roughnesses of the dielectric layer 6b prepared by controllingthe coating conditions of the dielectric layer 6b and also in the casewhen no dielectric layer was provided.

                                      TABLE 8                                     __________________________________________________________________________                Film thickness            Surface roughness**                                 Diffusion                 Diffusion                                       White-                                                                            reflection                                                                         Dielectric           reflection                                                                         Dielectric                         Reference No.                                                                         ness                                                                              layer                                                                              layer Environment                                                                           Resistivity***                                                                       layer                                                                              layer                              __________________________________________________________________________    Example 22                                                                            70  4 μm                                                                            1 μm                                                                             25° C./ 50% RH                                                                 5 × 10.sup.13 Ωcm                                                        1.5 μm                                                                          1.2 μm                                  "   "    "     15° C./10% RH                                                                  5 × 10.sup.14 Ωcm                                                        "    "                                          "   "    "     35° C./85% RH                                                                  5 × 10.sup.12 Ωcm                                                        "    "                                  Comparative                                                                           70  4 μm                                                                            3 μm                                                                             25° C./50% RH                                                                  5 × 10.sup.13 Ωcm                                                        1.5 μm                                                                          0.05 μm                         Example 14                                                                            "   "    "     15° C./10% RH                                                                  5 × 10.sup.14 Ωcm                                                        "    "                                          "   "    "     35° C./85% RH                                                                  5 × 10.sup.12 Ωcm                                                        "    "                                  Comparative                                                                           70  4 μm                                                                            none  25° C./50% RH                                                                  5 × 10.sup.13 Ωcm                                                        1.5 μm                                                                          --                                 Example 15                                                                            "   "    "     15° C./10% RH                                                                  5 × 10.sup.14 Ωcm                                                        "    --                                         "   "    "     35° C./85% RH                                                                  2 × 10.sup.11 Ωcm                                                        "    --                                 __________________________________________________________________________             Initial stage       After successive copying*                                       Nondisplay                                                                            Display     Nondisplay                                                                            Display                                           portion portion     portion portion                            Reference No.                                                                          Contrast                                                                            whiteness                                                                             whiteness                                                                           Contrast                                                                            whiteness                                                                             whiteness                          __________________________________________________________________________    Example 22                                                                             70    70      0     67    67      0                                           70    70      0     67    67      0                                           70    70      0     67    67      0                                  Comparative                                                                            70    70      0     53    53      0                                  example 14                                                                             70    70      0     45    45      0                                           70    70      0     53    53      0                                  Comparative                                                                            70    70      0     50    50      0                                  example 15                                                                             70    70      0     50    50      0                                           70    70      0      0    50      50                                 __________________________________________________________________________     *After successive copying; after 10000 repeated display                       **Surface roughness: 10 point average roughness Rz                            ***Resistivity                                                                ##STR7##                                                                      S: measured area,                                                             t: film thickness (diffusion reflection layer thickness) plus (dielectric     layer thickness)                                                         

EXAMPLE 23

In this Example, the image holding member 5 was formed by vapordepositing aluminum with a film thickness of 800Å onto the surface of apolyester film with a thickness of 100 μm, applying a coating materialto a thickness of 30 μm according to the coating step shown below toform a coating as the diffusion reflection layer 6a with a surfaceroughness of 1.5 μm. More specifically, coating of the coating materialhas performed by dispersing 54 parts by weight of barium sulfate powderwith an average particle size of 1.0 μm and 30 parts by weight of athermosetting phenol resin together with 810 parts by weight of methanolin a ball mill for 10 hours, coating the resulting dispersion with anaverage dispersed particle size of 1.5 μm by a reverse roll coater,followed by heating at 140° C. for 5 minutes.

Next, a coating material with a viscosity of 30 cps comprising 10 wt. %of a soluble vinyl chloridevinyl acetate resin (number average molecularweight 4×10⁴) and 90 wt. % of methyl ethyl ketone was coated by areverse roll coater under the conditions of a coating speed of 4 m/min.and a gap of 10 μm and dried at 140° C. for 5 minutes to provide adielectric layer with a film thickness of 1 μm on the previous whitefilm of the diffusion reflection layer 6a, thus preparing an imageholding member 5 having a surface roughness of 1.2 μm.

Table 9 shows the recording and displaying characteristics of the imageholding member 5 together with those in Examples 24, 25 and Comparativeexample 16 with different surface roughnesses (0.4 μm, 0.1 μm) of thedielectric layer 6b prepared by controlling the coating conditions ofthe dielectric layer 6b.

                                      TABLE 9                                     __________________________________________________________________________                Film thickness            Surface roughness**                                 Diffusion                 Diffusion                                       White-                                                                            reflection                                                                         Dielectric           reflection                                                                         Dielectric                         Reference No.                                                                         ness                                                                              layer                                                                              layer Environment                                                                           Resistivity***                                                                       layer                                                                              layer                              __________________________________________________________________________    Example 23                                                                            70  4 μm                                                                            1 μm                                                                             25° C./50% RH                                                                  5 × 10.sup.13 Ωcm                                                        1.5 μm                                                                          1.2 μm                          Example 24                                                                            70  4 μm                                                                            2 μm                                                                             "       5 × 10.sup.13 Ωcm                                                        1.5 μm                                                                          0.4 μm                          Example 25                                                                            70  4 μm                                                                            3 μm                                                                             "       5 × 10.sup.13 Ωcm                                                        1.5 μm                                                                          0.1 μm                          Comparative                                                                           70  4 μm                                                                            4 μm                                                                             "       5 × 10.sup.13 Ωcm                                                        1.5 μm                                                                          0.05 μm                         Example 16                                                                    __________________________________________________________________________             Initial stage       After successive copying*                                       Nondisplay                                                                            Display     Nondisplay                                                                            Display                                           portion portion     portion portion                            Reference No.                                                                          Contrast                                                                            whiteness                                                                             whiteness                                                                           Contrast                                                                            whiteness                                                                             whiteness                          __________________________________________________________________________    Example 23                                                                             70    70      0     67    67      0                                  Example 24                                                                             70    70      0     67    67      0                                  Example 25                                                                             70    70      0     65    65      0                                  Comparative                                                                            70    70      0     53    53      0                                  example 16                                                                    __________________________________________________________________________     *After successive copying; after 10000 repeated display                       **Surface roughness: 10 point average roughness Rz                            ***Resistivity                                                                ##STR8##                                                                      S: measured area,                                                             t: film thickness (diffusion reflection layer thickness) plus (dielectric     layer thickness)                                                         

EXAMPLE 26

In this Example, the image holding member 5 was formed by vapordepositing aluminum with a film thickness of 800Å onto the surface of apolyester film with a thickness of 100 μm, applying a coating materialto a thickness of 30 μm according to the coating step shown below toform a coating as the diffusion reflection layer 6a with a surfaceroughness of 1.5 μm. More specifically, coating of the coating materialwas performed by dispersing 54 parts by weight of the reducing typeelectroconductive zinc oxide powder with an average particle size of 1.0μm and 30 parts by weight of a thermosetting phenol resin together with700 parts by weight of methyl ethyl ketone in a ball mill for 10 hours,coating the resulting dispersion with an average dispersed particle sizeof 1.2 μm by a reverse roll coater, followed by heating at 140° C. for 5minutes. The diffusion reflection layer 6a was found to have aresistivity of 1×10⁹ Ω·cm (25° C./50% RH).

Next, a coating material with a viscosity of 30 cps comprising 10 wt. %Of a soluble vinyl chloride-vinyl acetate resin (number averagemolecular weight 4×10⁴) and 90 wt. % of methyl ethyl ketone was coatedby a reverse roll coater under the conditions of a coating speed of 4m/min. and a gap of 10 μm and dried at 140° C. for 5 minutes to providea dielectric layer 6b with a film thickness of 1 μm on the previouswhite film of the diffusion reflection layer 6a, thus preparing an imageholding member 5 having a surface roughness of 1.2 μm.

Table 10 shows the recording and displaying characteristics of the imageholding member 5 together with those in Examples and Comparativeexamples with thicker film thicknesses of the dielectric layer 6bprepared by controlling the coating conditions of the dielectric layer.

Also, Table 10 shows the recording and displaying characteristics ofExamples and Comparative examples with different resistivities of thediffusion reflection layer 6a prepared by varying the composition ratio(see Table 11) of the reducing type electroconductive zinc oxide used inthe diffusion reflection layer 6a in Example 26.

                                      TABLE 10                                    __________________________________________________________________________                Film thickness                                                                Diffusion                                                                 White-                                                                            reflection                                                                         Dielectric                                                   Reference No.                                                                         ness                                                                              layer                                                                              layer Environment                                                                            Resistivity***                                __________________________________________________________________________    Example 26                                                                            94  30 μm                                                                           1 μm                                                                             25° C./50% RH                                                                   1 × 10.sup.13 Ωcm                         "   "    "     15° C./10% RH                                                                   1 × 10.sup.14 Ωcm                         "   "    "     35° C./85% RH                                                                   1 × 10.sup.12 Ωcm                 Example 27                                                                            94  30   3     25° C./50% RH                                                                   1 × 10.sup.13 Ωcm                 Example 28                                                                            94  30   5     25° C./50% RH                                                                   1 × 10.sup.13 Ωcm                 Example 29                                                                            94  30   7     25° C./50% RH                                                                   1 × 10.sup.13 Ωcm                 Comparative                                                                           94  30   10    25° C./50% RH                                                                   1 × 10.sup.13 Ωcm                 Example 17                                                                    __________________________________________________________________________            Initial stage    After successive copying*                                         Nondisplay                                                                           Display   Nondisplay                                                                          Display                                                portion                                                                              portion   portion                                                                             portion                                   Refrence No.                                                                          Contrast                                                                           whiteness                                                                            whiteness                                                                          Contrast                                                                           whiteness                                                                           whiteness                                 __________________________________________________________________________    Example 26                                                                            94   94     0    89   89    0                                                 94   94     0    89   89    0                                                 94   94     0    89   89    0                                         Example 27                                                                            94   94     0    89   89    0                                         Example 28                                                                            94   94     0    89   89    0                                         Example 29                                                                            89   94     5    74   89    5                                         Comparative                                                                           64   94     30   59   89    30                                        example 17                                                                    __________________________________________________________________________     *After successive copying; after 10000 repeated display                       ##STR9##                                                                      S: measured area,                                                             t: film thickness (diffusion reflection layer thickness) plus (dielectric     layer thickness)                                                         

                  TABLE 11                                                        ______________________________________                                                                 Diffusion                                                                     reflection                                                  Composition       layer                                                       Reducing type                                                                             Thermoset-                                                                              Inherent                                                electroconductive                                                                         ting phenol                                                                             electric                                                zinc oxide powder                                                                         resin     resistivity                                      ______________________________________                                        Example 30                                                                             120 parts by weight                                                                         30        1 × 10.sup.7 Ω ·                                         cm                                           Example 31                                                                             90 parts by weight                                                                          30        1 × 10.sup.8 Ω ·                                         cm                                           Example 32                                                                             30 parts by weight                                                                          30        1 × 10.sup.12 Ω ·                                        cm                                           Comparative                                                                            15 parts by weight                                                                          30        1 × 10.sup.13 Ω ·                                        cm                                           example 18                                                                    Comparative                                                                            10 parts by weight                                                                          30        1 × 10.sup.14 Ω ·                                        cm                                           example 19                                                                    ______________________________________                                    

                                      TABLE 12                                    __________________________________________________________________________            Film thickness                                                                    Diffusion                                                                 White-                                                                            reflection                                                                         Dielectric                                                   Reference No.                                                                         ness                                                                              layer                                                                              layer Environment                                                                            Resistivity***                                __________________________________________________________________________    Example 33                                                                            94  30 μm                                                                           1 μm                                                                             25° C./50% RH                                                                   1 × 10.sup.13 Ωcm                 Example 34                                                                            94  30   1     25° C./50% RH                                                                   1 × 10.sup.13 Ωcm                 Example 35                                                                            94  30   1     25° C./50% RH                                                                   1 × 10.sup.13 Ωcm                 Comparative                                                                           94  30   1     25° C./50% RH                                                                   2 × 10.sup.13 Ωcm                 Example 20                                                                    Comparative                                                                           94  30   1     25° C./50% RH                                                                   2 × 10.sup.13 Ωcm                 Example 21                                                                    __________________________________________________________________________            Initial stage    After successive copying*                                         Nondisplay                                                                           Display   Nondisplay                                                                          Display                                                portion                                                                              portion   portion                                                                             portion                                   Reference No.                                                                         Contrast                                                                           whiteness                                                                            whiteness                                                                          Contrast                                                                           whiteness                                                                           whiteness                                 __________________________________________________________________________    Example 33                                                                            94   94     0    89   89     0                                        Example 34                                                                            94   94     0    89   89     0                                        Example 35                                                                            84   94     0    79   89    10                                        Comparative                                                                           54   94     40   49   89    40                                        example 20                                                                    Comparative                                                                           34   94     60   29   89    60                                        example 21                                                                    __________________________________________________________________________     *After successive copying; after 10000 repeated display                       ##STR10##                                                                     S: measured area,                                                             t: film thickness (diffusion reflection layer thickness) plus (dielectric     layer thickness)                                                         

EXAMPLE 36

On the surface of a polyester film with a thickness of 100 μm, aluminumwas vapor deposited with a film thin thickness of 800Å and a coatingmaterial was applied according to the coating described below to athickness of 30 μm to form a diffusion reflection layer 6a.

Coating

54 parts by weight of antimony oxide powder with an average particlesize of 1.0 μm and 30 parts by weight of a thermosetting phenol resintogether with 700 parts by weight of methyl ethyl ketone were dispersedin a ball mill for 10 hours, coating the resulting dispersion with anaverage dispersed particle size of 1.0 μm by a reverse roll coater,followed by heating at 140° C. for 5 minutes. The diffusion reflectionlayer 6a was found to have a resistivity of 1×10⁸ Ω·cm (25° C./50% RH).

Next, a coating material with a viscosity of 30 cps comprising 10 wt. %of a soluble acrylic resin (number average molecular weight 4×10⁴) and90 wt. % of methyl ethyl ketone was coated by a reverse roll coaterunder the conditions of a coating speed of 4 m/min. and a gap of 10 μmand dried at 140° C. for 5 minutes to provide a dielectric layer 6b witha film thickness of 1 μm on the previous white film of the diffusionreflection layer 6a, thus preparing an image holding member 5.

In Example 37, Comparative examples 22, 23, the resin in the dielectriclayer 6b was replaced with the soluble type vinyl alcohol resin, thesoluble type vinyl-pyridine resin and the soluble type polyacrylicquaternary amine resin, and coated in the same manner as in Example 35to form the image holding members 5, respectively.

The recording and displaying characteristics as the respective imageholding members are shown in Table 13.

Example 37: the soluble type vinyl alcohol resin for dielectric layer;

Comparative example 22: the soluble type vinyl-pyridine resin fordielectric layer:

Comparative example 23: the soluble type polyacrylic quaternary amineresin.

                                      TABLE 13                                    __________________________________________________________________________                Film thickness                                                                Diffusion                                                                 White-                                                                            reflection                                                                         Dielectric                                                   Reference No.                                                                         ness                                                                              layer                                                                              layer Environment                                                                            Resistivity***                                __________________________________________________________________________    Example 36                                                                            93  30 μm                                                                           1 μm                                                                             25° C./50% RH                                                                   1 × 10.sup.14 Ωcm                 Example 37                                                                            93  30   1     25° C./50% RH                                                                   1 × 10.sup.12 Ωcm                 Comparative                                                                           93  30   1     25° C./50% RH                                                                   2 × 10.sup.11 Ωcm                 Example 22                                                                    Comparative                                                                           93  30   1     25° C./50% RH                                                                   2 × 10.sup.9 Ωcm                  Example 23                                                                    __________________________________________________________________________            Initial stage    After successive copying*                                         Nondisplay                                                                           Display   Nondisplay                                                                          Display                                                portion                                                                              portion   portion                                                                             portion                                   Reference No.                                                                         Contrast                                                                           whiteness                                                                            whiteness                                                                          Contrast                                                                           whiteness                                                                           whiteness                                 __________________________________________________________________________    Example 36                                                                            93   93      0   88   88     0                                        Example 37                                                                            88   93      5   83   88     5                                        Comparative                                                                           68   93     25   63   88    25                                        example 22                                                                    Comparative                                                                           23   93     70   18   88    70                                        example 23                                                                    __________________________________________________________________________     *After successive copying; after 10000 repeated display                       ##STR11##                                                                     S: measured area,                                                             t: film thickness (diffusion reflection layer thickness) plus (dielectric     layer thickness)                                                         

The image holding member of the present invention is not required tosatisfy both of the conditions of 10-point average roughness andelectrical resistance of the above dielectric layer, but either one maybe satisfied. These are also apparent from the Examples of Example 14 etseq.

The present invention comprises the above constitution and action, andcan form a display surface excellent in whiteness with a diffusionreflection layer and can improve contrast.

Also, by laminating a dielectric layer on the diffusion reflection layersurface, unevenness on the diffusion reflection layer surface can beremoved, and also progress of water into the diffusion reflection layercan be prevented by the dielectric layer, whereby the environmentalcharacteristics can be improved, and also durability can be improved.

Further, since the electrical resistance is made smaller than that ofthe dielectric layer, the charges in the diffusion reflectiOn layer canbe decayed quickly to prevent contrast lowering during repeated uses,etc. and maintain good stable image quality.

Further, when the surface roughness of the dielectric layer is setwithin the range of 0.1 to 0.5 μm, good image quality can be maintainedover a long term.

We claim:
 1. An image holding member for holding granular dry processdeveloper through electrical adsorption force, comprising from the sidefor holding the dry process developer:a dielectric layer; a diffusionreflection layer having reflective fine particles dispersed in a resin:and an electroconductive layer, said dielectric layer being made to havea ten-point average roughness of 0.1 μm to 5.0 μm.
 2. An image holdingmember according to claim 1, wherein the ten-point average roughness ofsaid dielectric layer is preferably 0.1 μm to 3.5 μm.
 3. An imageholding member according to claim 1, wherein said dielectric layer isconstituted mainly of a resin and a substance for lowering electricalresistance is further added thereto.
 4. An image holding member forholding granular dry process developer through electrical adsorptionforce, comprising from the side for holding the dry process developer:adielectric layer; a diffusion reflection layer having reflective fineparticles dispersed in a resin; and an electroconductive layer; whereinsaid diffusion reflection layer has an electrical resistance smallerthan an electrical resistance of said dielectric layer, and saiddielectric layer has ten-point average roughness from 0.1 μm to 5.0 μm.5. An image holding member according to claim 4, herein the ten-pointaverage roughness of said dielectric layer is preferably 0.1 μm to 3.5μm.
 6. An image holding member according to claim 4, wherein saiddielectric layer is comprised mainly of a resin, and a substance forlowering electrical resistance is further added thereto
 7. An imageholding member for holding granular dry process developer throughelectrical adsorption force, comprising from the side for holding thedry process developer:a dielectric layer; a diffusion reflection layerhaving reflective fine particles dispersed in a resin; and anelectroconductive layer, wherein said diffusion reflection layer has anelectrical resistance smaller than an electrical resistance of thedielectric layer.
 8. An image holding member according to claim 7,wherein said dielectric layer is comprised mainly of a resin, and asubstance for lowering electrical resistance is further added thereto.9. An image forming device for adsorbing granular dry process developeronto an image holding member through electrical adsorption forcecomprising:an image holding member comprising from a side for holdingthe dry process developer, a dielectric layer and a diffusion reflectionlayer having reflective fine particles dispersed in a resin, with saiddielectric layer being made to have a ten-point average roughness of 0.1μm to 5.0 μm; moving means for moving said image holding member;recording electrodes arranged in a direction crossing a moving directionof said image holding member; means for feeding an electroconductivedeveloper disposed between said image holding member and said recordingelectrodes; and means for applying signal voltages to said recordingelectrodes.
 10. An image forming device according to claim 9, furtherhaving a display portion for dispensing the visible image formed with adeveloper on said image holding member.
 11. An image forming device foradsorbing granular dry process developer onto an image holding memberthrough electrical adsorption force comprising:an image holding membercomprising from a side for holding the dry process developer, adielectric layer and a diffusion reflection layer having reflective fineparticles dispersed in a resin, wherein said diffusion reflection layerhas an electrical resistance smaller than that of said dielectric layer,and also said dielectric layer being made to have a ten-point averageroughness of 0.1 μm to 5.0 μm; moving means for moving said imageholding member; recording electrodes arranged in a direction crossing amoving direction of said image holding member; means for feeding anelectroconductive developer between said image holding member and saidrecording electrodes; and means for applying signal voltages to saidrecording electrodes.
 12. An image forming device according to claim 11,having a display portion for displaying the visible image formed with adeveloper on said image holding member.
 13. An image forming device foradsorbing granular dry process developer onto an image holding memberthrough electrical adsorption force comprising:an image holding membercomprising from a side for holding the dry process developer, adielectric layer and a diffusion reflection layer having reflective fineparticles dispersed in a resin, wherein said diffusion reflection layerhas an electrical resistance smaller than that of said dielectric layer,moving means for moving said image holding member; recording electrodesarranged in a direction crossing a moving direction of said imageholding member; means for feeding an electroconductive developer betweensaid image holding member and said recording electrodes; and means forapplying signal voltages on said recording electrodes.
 14. An imageforming device according to claim 13, having a display portion fordisplaying the visible image formed with a developer on said imageholding member.